Density Altitude Calculator
Enter the pressure altitude in feet and the outside air temperature in Celsius to estimate density altitude, the altitude the aircraft feels in terms of air density. The calculator also shows the standard ISA temperature at that altitude.
How to calculate density altitude
- Set your altimeter to 29.92 to read pressure altitude, then enter it in feet.
- Enter the outside air temperature in degrees Celsius.
- Read the density altitude and the standard ISA temperature.
Examples
Hot day at a mountain strip
PA = 5000 ft, OAT = 25 C
ISA 5.1 C, density altitude 7388 ft
Standard day at sea level
PA = 0 ft, OAT = 15 C
ISA 15 C, density altitude 0 ft
Frequently asked questions
What is density altitude?
Density altitude is pressure altitude corrected for temperature. It is the altitude at which the air density would be standard, and it is what aircraft performance actually depends on.
What formula does this calculator use?
It uses the cockpit approximation: ISA temperature = 15 - 1.98 * (pressure altitude / 1000), then density altitude = pressure altitude + 120 * (OAT - ISA temperature).
Why does high density altitude reduce performance?
Thinner air means less lift, less thrust and less engine power. On hot days at high elevation, density altitude can be thousands of feet above the field, lengthening takeoff and cutting climb rate.
How accurate is this approximation?
The 120 ft per degree rule is the standard pilot estimate and is close to the exact ICAO value over normal conditions. For precise performance planning use the aircraft flight manual charts.
What is pressure altitude?
Pressure altitude is the altitude shown when the altimeter is set to the standard 29.92 inHg (1013.25 hPa). It removes local pressure variation so density altitude can be computed from temperature alone.
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